Squeak Etoys is a "media authoring tool"-- software that you can download to your computer
and then use to create your own media. You can write out your project and share it with others.
Etoys runs on any Mac or Windows machine, as well as on the OLPC XO machine.
It is free.
Find out about Etoys.

Text of this guide (for searching): Halo Tools: Center of Rotation
Every object has a center of rotation.
The center can be moved to any
place on the screen.
Click the green clock
to start the script. Open a halo for the bot's left arm and find the center-of-rotation handle, a small blue circle with red crosshairs inside.
Hold down the Shift key and drag the red + to a new place. For objects that are not Sketches, rotate the blue
Halo handle to
see the
direction and
center controls. + The red + marks the bot's new center of rotation. The center of rotation can be far from the center of the drawing.
Click the green clock to try this script.